Thiazoles herbicidal

ABSTRACT

Certain novel amides of at least three carbon atoms, which are substituted on the nitrogen by a thiazol-2-yl moiety, useful as herbicides.

United States Patent [191 Pilgram et al.

[ Nov. 12, 1974 i 1 THIAZOLES HERBICIDAL [75] Inventors: Kurt H. Pilgram; Richard D. Skiles,

both of Modesto, Calif.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: Nov. 7, 1972 [2l] Appl. No.: 304,423

Related US. Application Data [62] Division of Sen No. 30,367, April 720, 1970, Pat. No.

[52 us. Cl. .Q ..71/90 51 Int. Cl A0ln9/12 [58] Field of Search 71/90 8/1972 Engelhart 71/90 X Primary ExaminerJames 0. Thomas, Jr.

[5 7] i I ABSTRACT Certain novel amides of at least three carbon atoms, which are substituted on the nitrogen by athiazol-Z-yl moiety, useful as herbicides.

6 Claims, N0 Drawings THIAZOLES HERBICIDAL This is a division, of applicatio nSer. No. 030,367, filed Apr. 20, 1970 now US. Pat. No. 3,717,651.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel class of herbicidal.

SUMMARY OF THE- INVENTION or sulfamoyl moiety and optionally substituted in the 4-position with an alkyl group, their use as herbicides and herbicidal formulations containing them.

DESCRIPTION OF THE PREFERRED EMBODIMENT The novel compounds of this invention can be described by the general formula:

wherein R represents hydrogen or alkyl or up to four carbon atoms; R' is alkyl of two to eight carbon'atoms, cyclic alkyl of up to eight carbon atoms, alkenyl of up to eight carbon atoms, or aryl, all of which may be unsubstituted or substituted by one or more of fluorine, chlorine, bromine, cyano or trifluoromethyl; R is hydrogen or alkyl of up to four carbon atoms; n is 0, l or 2; R is hydrogen, alkyl of up to four carbon atoms, cy-

clic alkyl of up to four carbon atoms or R wherein R represents hydrogen, alkyl of up to four carbon atoms or cyclic alkyl of up to four carbon atoms; R is any of the moieties represented by R or a lower alkali metal ion (Na, K or Li) or R C(O) wherein R is alkyl of up to three carbon atoms; R also represents alkoxy of up to three carbon atorns or wherein R and R are hydrogen or alkyl of up to three carbon atoms when R is hydrogen or alkyl of up to three carbon atoms; R and R together also may form an alkylene group. Any of these alkyl groups may be of either branched-chain or straight-chain configuration.

Eitemplary species of the class of the invention include:

N (4-rnethyl-5 (dimethylsulfamoyl)thiazol-2- yl)cyclopropanecarboxamide, N(S-(dimethylsulfamoyl)thiazol-2-yl)cyclopropanecarboxamide, N---(4-rnethyl-5-(dimethylsulfamoyl)thiazol-Z- yl)propiorramide, N(S-(dimethyl'sulfamoyl)thiazol-2- yl)propionamide, N-(5-(dimethylhydrazinosulfonyl)thiazol-2- yl)cyclopropanecarboxamide, N (S-(methylsulfamoyl)thiazol-Z-yl)cyclopropanecarboxamide, N(5-(methylsulfamoyl)thiazol-2-y1)propionamide,

Sodium salt of N-(5-(methylsulfamoy1)thiazo1-2- yl)cyclopropanecarboxamide, Sodium salt of N(5-(methylsulfamoyl)thiazol-2- yl)propionamide, Potassium salt of N(Smethylsulfamoyl 2-yl)cyclo- I propanecarboxamide,

Potassium salt of N(5-(methylsulfamoyl)thiazol-Z- yl)propionamide, N(5-(aziridinylsulfonyl)thiazol-2-yl)cyclopropanecarboxamide, N(5-(methylthio)thiazol-2-yl)-2- methylacrylamide, N(5-(methylsulfinyl)thiazol-2-yl)-2- methylacrylamide, N(5-(methylsulfonyl)thiazol-Z-yl)-2- methylacrylarnide, N(5-(methylthio)thiazol-2 yl)-3,3- bis(trifluoromethyl)acrylamide, N-(S-methylthio)thiazol-2-yl)-2-cyanocyclopropanecarboxamide, N(5-(methylthio)thiazol-2-yl)cyclopentanecarboxamide, N. (5-(methylsulfonyl)thiazol-2-yl)cyclopentanecarboxamide, N-(5-(methylthio)thiazol-2-yl)-3,4- H dichlorobenzamide, N(S-(methylsulfonyl)thiazol-2-yl)-3,4-

dichlorobenzamide, N(S-(methylsulfonyl)thiazol-2-yl)octanamide, N(5-(methylsulfonyl)thiazol-2-yl)-2,2-dimethylpentamide, N(5-(methylthio)thiazol-2-yl)-3-methyl-5,5-dimethylhexanamide The highest herbicidal activity appears to be associated with the subclass wherein R represents hydrogen or alkyl, R is alkyl or cyclic alkyl, R is hydrogen or methyl, R is alkyl, cyclic alklyl or wherein R and R represent hydrogen or alkyl of up to three carbon atoms, n is 0, l or 2. Preferred species of this subclass include compounds wherein R and R represent hydrogen or methyl, R is alkyl of two to five carbon atoms or cyclic alkyl of up to four carbon atoms, R is alkyl of up to three carbon atoms.

Specific examples of the preferred subclass include:

N 5 -(methylthio )thiazol-2-yl )propionamide;

N(S-(methylsulfonyl )thiazol-2-yl)propionamide,

N-(4-methyl-5-(methylthio)thiazol-2- yl )propionamide,

N(4-methyl-5-(methylsulfonyl )thiazol-Z- yl)propionamide,

N (5-( ethylthio)thiazol-Z-yl)propionamide,

N(5-( ethy'lsulfonyl)thiazol-Z-yl )propionamide,

N S-(isopropylsulfonyl)thiazol-2-yl)proionamide,

N(5-( isopropylthio )thiazol-2-yl )propionamide,

N- 5-( isopropylsulfonyl)thiazol-2- yl)propionamide,

N 5-( methylthio )thiazol-2-yl)-2- methylpropionamide,

N( S-(methylsulfonyl )thiazol-2-yl)-2- methylpropionamide,

N- 5-(methylthio)thiazol-2-yl )cyclopropanecarboxamide,

N-(5-(methylsulfonyl)thiazol-Z-yl)cyclopropanecarboxamide,

N( 5-( methylsulfinyl)thiazol-2-yl)cyclopropanecarboxamide,

N(4-methyl-5-(methylthio )thiazol-'2-yl)cyclopropanecarboxamide,

N(4-methyl-5-(methylsulfonyl )thiazol-2-yl)cyclopropanecarboxamide,

N(5-(methylthio)thiazol-2-yl)-1-methylcyclopropanecarboxamide,

N 5-( methylsulfonyl )thiazol-2-yl)- l -methylcyclopropanecarboxamide,

N- S-(ethylthio )thiazol-2-yl)cyclopropanecarboxamide,

N- 5-(ethylsulfonyl)thiaZol-2-yl)cyclopropanecarboxamide,

N 5 isopropylthio)thiazol-Z-yl )cyclopropanecarboxamide,

N(5-( isopropylsulfonyl )thiaZol-2-yl)cyclopropanecarboxamide,

N- 5-(methylthio)thiazol-Z-yl)-2,2-dimethylpropionamide,

N(S-(m ethylsulfonyl )thiazol-Z-yl )-2,2-dimethylpropionamide,

N( 5-( methylthio )thiazol-Z-yl)cyclobutanecarboxamide, I

N 5-( methylthio)thiazol-2-yl )-2- methylpentanamide,

N(5-( ethylthio)thiazol-2-yl)-2- methylpentanamide,

N(5-(isopropylthio)thiazol-2-yl )2- methylpentanamide,

N 5-(methylsulfonyl)thiazol-2-yl)-2- methylpentanamide,

N(5-( ethylsulfonyl )thiazol-2-y])-2- methylpentanamide,

N(S-(isopropylsulfonyl )thiazol-2-yl)-2- methylpentanamide,

N-methyl-N-( 4-methyl-5-(methylsulfonyl )thiazol-2- yl)cyclopropanecarboxamidc,

N-methylN-(4-methyl-5-(methylthio)thiazol-2- yl)cyclopropanecarboxamide,

N-methyl--N-(4-methyl-5-(methylthio)thiazol-2- yl)propionamide, I

N-methylN(4-methyl-5-(methylsulfonyl)thiazol- 2-yl)propionamide,

N(4-methyl-5-(ethylthio)thiazol-2-yl)cyclopropanecarboxamide,

N-(4-methyl-5-(ethylsulfonyl)thiazol-2-yl)cyclopropanecarboxamide,

The compounds of this invention are solid at ambient temperature. They may be suitably formulated for use as herbicides, as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions and pastes. Wettable powders are usually compounded to contain 25, 50, 75, or up to percent of toxicant and usually contain, in addition to solid carrier, 3-1O percent of a dispersing agent and, where necessary, 0-l0 percent of stabilizer(s) and/or other additives such aspenetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing /2 to 10 percent of toxicant. Granules are usually prepared to have a size between 10 and BS mesh, and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain /2-25 percent of toxicant plus additives such as stabilizers, slow-release modifiers, binding agents, etc. Emulsifiable concentrates usually contain, in addition to the solvent, and, when necessary, co-solvent, 10-50 percent s/v toxicant, 2-20 percent w/v emulsifiers and 0-2O percent of appropriate additives such as stabilizers, penetrants and corrosion inhibitors. Pastes are compounded so as to obtain a stable flowable product and usually contain 10-60 percent toxicant, 2-20 percent of appropriate additives and, as carrier, water or an organic liquid in which toxicant is substantially insoluble. Except where indicated otherwise,'all percentages given in this paragraph are percentages by weight.

The herbicidal compounds of this invention may be prepared by the reaction of the substituted 2 aminothiazole of formula II:

wherein R, R and R are as defined above, with an acyl halide of the formula R COHal in which R is as defined above and Hal representsa halogen atom, preferably chlorine. The reaction is suitably carried out in the presence of a base such as a tertiary amine or pyridine. The base serves as an acid scavenger for the hydrogen halide which is formed. The reaction is run in an anhydrous solvent such as tetrahydrofuran or ether substituted or 4-alkyl substituted 2-aminothiazole intermediate.

The 2-aminothiazole intermediate is then treated with an appropriate halogenating agent to yield a halo-2-aminothiazole. This reaction can be successfully I carried out in solvents such as water aqueous acids,

chloroform, carbon tetrachloride, benzene, carbon disulfide and glacial acetic acid using agents such as iodine, bromine, chlorine or sulfuryl chloride.

The reaction of the halogenated 2-aminothiazole intermediate with a sodium mercaptide will yield the desired 5-thio-2-aminothiazole by replacement of the halogen. This reaction is suitably carried out in refluxing methanol. If an alkylthio compound is desired, the appropriate sodium alkylmercaptide should be used.

This thio compound can be oxidized to the sulfinyl derivative by treatment with meta-chloroperbenzoic acid in chloroform solution. The sulfonyl derivative is prepared similarly using an excess of 33 percent hydro gen peroxide in glacial acetic acid or acetone solution.

5-sulfamoyl derivatives may be prepared by reacting an acylated 2-aminothiazole, optionally substituted in the 4-position with alkyl groups, with excess chlorosulfonic acid and phosphorus pentachloride to yield the 5-chlorosulfony1 intermediate. This 5-chlorosulfonyl intermediate is then reacted with the appropriate prisired S-sulfamoyl derivative.

The compounds of the invention, processes for their preparation and their herbicidal activity, are illustrated by the following examples, in which parts by weight (w) and parts by volume (v) bear the same relation as the kilogram to the liter and all temperatures are in degrees centigrade.

EXAMPLE 1 N(5-(ethylthio )thiazo1-2-yl )propionamide mary or secondary amine or ammonia to yield the deluted with 200 v of acetone and cooled to 5. The re- 7 sulting precipitate was filtered, washed well with acetone and air dried. This solid (202 w) was suspended in water (800 v) and cooled to 5. Sodium hydroxide (52 w) in water (50 v) containing sodium hydrosulfite (1.0 w) was added dropwise. The mixture was stirred at 5 for 1 hour and filtered to yield 2-amino-5- bromothiazole (188 w) melting at l04l05.

A mixture of 2-amino-5-bromothiazole w), ether (200 v) and ethyl mercaptan (15.5 w) was treated with a solution of sodium methoxide (13.5 w) in absolute methanol v) over a period .of 15 minutes. The exothermic reaction raised the temperature to 40 and a fine solid precipitated. The reaction mixture was stirred at ambient temperature for 1 hour and washed with water (3 X v). The organic fraction was dried with MgSO, and concentrated by distillation in a vacuum to yield a red solid. This residue was extracted with boiling hexane and the solution was chilled to yield 2-amino-5-(ethylthio)thiazole (25 w) melting at 7375. The structure was confirmed by infrared spectrum analysis.

To a mixture of 2-amino-5-(ethylthio)thiazole (6 w), tetrahydrofuran (50 v) and triethylamine (3.8 w), pro pionyl chloride (3.5 w) was added dropwise. The addition produced a precipitate and was exothermic to 45. The reaction mixture was stirred at ambient temperature for 30 minutes and poured into ice water. The solid was collected on a filter and dried to yield N-(5- (ethylthio)thiazol-2-yl)propionamide (7.3 w) m.p. 153155. The structure was confirmed by elemental and infrared analyses.

Analysis (Percent by Weight) Calculated: N-l 3.0 S-29.6 Found: N-13.2 S-29.5

EXAMPLE II N( 5 ethylsulfonyl )thiazol-2-yl )propionamide analyses.

Analysis (Percent by Weight) Calculated: N-ll.3 S-25.8 Found: N-1'1.2 S-25.9

EXAMPLE III N-(4-methyl-5-(methylthio)thiazol-2- yl)propionamide ll oHts- -NHg-oH1cH= filter cake was dissolved in a minimum amount of cold water and treated with aqueous ammonia until pH of 8 was obtained. The solid wasfiltered and dried to yield 2-amino-5-bromo-4-methylthiazole (55 w) melting at l04-106. The structure was confirmed by infrared spectrum analysis.

A solution of 2-amino-5-bromo-4-methylthiazole (45 w) in absolute methanol (150 v) was stirred during the addition of a solution of sodium methoxide (12.6 w) and methyl mercaptan (11.2 w) in absolute methanol (100 v). After completion of the addition minutes), the reaction mixture was heated to reflux (64) for 2.5 hours, left at ambient temperature for 18 hours, poured over ice, and extracted with methylene chloride (3 X 150 v). The combined extracts were dried with magnesium sulfate and concentrated by distillation in a vacuum to a red solid. The residue was recrystallized from hexane-benzene (3:2) to yield 2-amino-4-methyl-5- (methylthio)thiazole (23 w) melting at 77-80. The structure was confirmed by elemental analysis.

To a mixture of 2-amino-4-methyl-5-(methylthio)- thiazole (12.7 w), tetrahydrofuran (100 v) and triethylamine (8.2 w), propionyl chloride (7.5 w) was added dropwise. The addition which was exothermic to 55 caused a solid to precipitate. The reaction product was cooled to ambient temperature, poured into ice water and filtered. The solid filter cake was recrystallized from methanol and then from ethanol to yield N-(4- methyl-5-(methylthio)thiazol-2-yl)propionamide (3 w) m.p. l26l27. The structure was confirmed by elemental and infrared analyses.

Analysis (Percent by Weight) Calculated: Nl3.0 S-29.6 Found: N-12.8 S-29.2

EXAMPLE 1V N- 4-methyl-5-(methylsulfonyl)thiazol-2- yl)propionamide (methylthio)thiazol-Z-yl)propionamide (2 w) in chloroform (50 v), 85% m-chloroperbenzoic acid was added. The solution was chilled during the addition and upon completion of the addition, the reaction mixture was allowed to stand at ambient temperatures for 18 hours. The reaction mixture was then washed with an aqueous solution of sodium carbonate (3 w in 15 v), after which the chloroform solution was dried and concentrated by distillation in a vacuum to 2 w of solid residue. The residuewas recrystallized from methanol to yield N(4-methyl-5-(methylsulfonyl)thiazol-2- yl)propionamide (1.3 w) m.p. 162164. The structure was confirmed by elemental and infrared spectrum analyses.

Analysis (Percent by Weight) Calculated: Found:

EXAMPLE V N(5-(dimethy1sulfamoyl)-thiazol-2-yl)propionamide CH3 O Analysis (Percent by Weight) Calculated: Found:

EXAMPLE VI Following procedures similar to those given in previous examples, the following other species of the compounds of the invention were prepared (symbols refer to formula Ill).

TABLE 1 T m Th R N 1 ll 1 l E MO) S N C R Analysis, percent P 'Suliur Nitrogen R R R. R. n 'o Calcd. Found Calcd. Fonud CH3 H C111 H 0 152-155 31.7 v 32.0 13.9 13.5 CH; H (31H; H 2 219-221 22. 4 26. 9 12. 0 11. 9 CH(CH3)2 H CzHs H 0 177-179 27. 8 27. 6 12. 5 12.5 CH(CH3)2 H CaH5 H 2 234-237 24.4 24.2 10.7 10.5

Nitrogen Found Calcd. Found TABLE l-(onlinued (O)n L U L 11m 11 Same as above. H H .do H d0.. H

CH3 CH CH:

Sameas above H 1 -'CHC3'H7 sameasabovehuuu H I CH2 '"CHZHJCHQ CH3 CH1 CH(CII3)2 am 9 L 11 EXAMPLE VII (no effect) to 9 (all dead) scale. The results are sum- Pre-emergence herbicidal activity of the typical commauled Table Post-emergence herbicidal activity was evaluated by spraying dilute suspensions of the test compound in a 1:1 mixture of acetone and water with 0.5 percent wet- I and l0 milligrams of test compound per tube, respecting agent on crabgrass (Digitaria sanguinalis) and pigtively. Seeds of watergrass (Echinochloa crusgalli) and weed plants (Amaranthus sp) grown under controlled cress (Lepidium sativum) were germinated in treated conditions atthe rates of. l and 10 pounds test comsoil under controlled conditions of temperature and pound per acre. After the plants were held for 10 to 11 light for 12 to 13 days prior to evaluation of'the effecdays, they were rated for treatment effect on a 0 (no tivencss of the treatments. At that time, the germinaeffect) to 9 (total plant kill) scale. The results of these tion was noted and the treatments were rated on a 0 tests are shown in Table II.

pounds of the invention was evaluated by planting weed seeds in soil held in large test tubes, the soil having been treated with the test compound at the rate of 11 TABLE 11 l I i 11 s o i N-'0"-R Pro-emergence Post-emergence Wat'ergrass Cress Crabgrass Pigweed 11 11 191 R4 n 1 10 1 10 1 10 1 10 0113 11- 02115 11 s 9 s 9 7 9 9 9 0111 11 02115 11 2 7 s 9 9 1 9 7 9 0111 0111 02115 11 9 s s 9 9 9 9 7 9 CH3 0113 02115 11 2 s s 9 9 9 9 7 9 C2115 H C2H5 H 0 8 8 8 8 9 9 9 9 C2115 II 02115 H 2 8 8 9 9 9 9 9 9 (01192011 11 02115 11 9 1 7 s s s 9 s 9 (01192011 11 02115 11 2 s s 9 9 6 s 9 9 0 a 11 011 01192 11 0 4 9 s 9 6 9 9 9 0111 11 011 0113 11 2 7 s 9 9 0 7 9 0111 11 1 I 11 0 7 9 9 9 7 9 e 9 CH1 CH1 Same as above. H 0 3 8 8 9 8 9 9 9 0111 H do H 1 7 9 9 9 7 9 9 9 0113 2 s s 9 9 9 9 7 9 0111 2 7 s 9 9 7 9 9 9 0111 0 1 7 s 9 4 7 1 7 0113 q o 2 s 6 s s 9 a 9 CH3 C111 11 Same as above H 2 6 8 8 9 6 8 l 9 02115 11 1 11 9 4 s s 9 s 9 s 9 Cells II Same as above. H 2 8 8 8 l 9 9 9 9 011(01192 11 do 11 0 5 7 s s 9 9 9 9 011(01191 11 1.0.90 11 2 s s s 9 9 9 9 9 0113 11 0101193 11 0 s 9 7 9 7 9 9 9 0111 11 0 01193 11 2 0 6 7 s 9 o 4 9 0111 11 1r 9 5 7 7 9 s 9 9 9 CH1 II Same as above. H 2 5 8 8 9 0 0 2 9 0111 .11 1111 11 0 s 7 s s a 9 9 9 01111. 11 Same as above. 11 0 2 s 7 s s 9 9 9 011 01192 11 d0 11 0 o o 5 s 7 s e 9 CH3 H H 2 8 8 9 9 9 9 l J (,zllr, 11 H 2 7 8 9 J U 9 7 U 011 01192 11 d 11 2 2 s s 9 .6 s 5 9 0113 0 o a s s 2 s s 9 011a 0113 (1111 0117 Same as above. CH3 2 3 7 9 9 2 6 4 9 PATENT NUMBER 3847588 F. 97

(111.1)2N ll (1 m ll 2 a 8 9 9 3 5 9 9 ((JllrOzN (1]!1 Calls ll 2 8 8 J J O 7 0 9 0mm 0m 02115 11 2 9 s a 9 9 6 9 9 11 2 7 s s 9 7 9 4 9 @3115 CH3 0.1115 0111 02115 11 0 s s 9 9 s 9 9 9 We claim as our invention: l. A herbicidal formulation comprising a herbicidally effective amount of a compound of the formula v a 1 a 11 R N O R3 (6) v J (J R1 wherein R and R is each hydrogen or alkyl of one to 5 four carbon atoms, together with an adjuvant therefor.

R2 1 wherein R represents hydrogen or alkyl of up to four 2. A method of controlling .weeds, which comprises carbon atoms, R is alkyl of two to eight carbon atoms, applying to the habitat a herbicidally effective amount cyclic alkyl of three to eight carbon atoms optionally of a compound of the formula substituted by phenyl or cyano, or alkenyl of two to eight carbon atoms optionally containing up to two trio fluoromethyl groups; n is 0, l or 2: R is hydrogen or J ll alkyl of up to four carbon atoms; R is alkyl of one to s R1 tum carbon atoms or.- 1

wherein R represents hydrogen or alkyl of up to four carbon atoms, R is alkyl of two to eight carbon atoms, cyclic alkyl of three to eight carbon atoms optionally substituted by phenyl or cyano, or alkenyl of two to eight carbon atoms optionally containing up to two trifluoromethyl groups; n is 0, l or 2; R is hydrogen or alkyl of up to four carbon atoms, R is alkyl of one to four carbon atoms or wherein R and R represent hydrogen or alkyl of up to three carbon atoms, n is O, 1 r 2.

4. A herbicidal composition according to claim 3 wherein R represents hydrogen or methyl; R is ethyl, isopropyl, cyclopropyl or l-methylbutyl; R is hydrogen; R is methyl, ethyl, isopropyl or dimethylamino; n is 0 or 2.

5. A method of controlling weeds according to claim 2 wherein R represents hydrogen or methyl, R is alkyl of two to five carbon atoms or cyclic alkyl of up to four carbon atoms, R is hydrogen or methyl, R is alkyl of up to three carbon atoms or wherein R and R represent hydrogen or alkyl of up to three carbon atoms, n is 0, l or 2.

6. A method of controlling weeds according to claim 5 wherein R represents hydrogen or methyl; R is ethyl, isopropyl, cyclopropyl or l-methylbutyl; R is hydrogeg; R 2is methyl, ethyl, isopropyl or dimethylamino; n 18 or 

1. A HERBICIDAL FORMULATION COMPRISING A HERBICIDALLY EFFECTIVE AMOUNT OF A COMPOUND OF THE FORMULA
 2. A method of controlling weeds, which comprises applying to the habitat a herbicidally effective amount of a compound of the formula
 3. A herbicidal composition according to claim 1 wherein R represents hydrogen or methyl, R1 is alkyl of two to five carbon atoms or cyclic alkyl of up to four carbon atoms, R2 is hydrogen or methyl, R3 is alkyl of up to three carbon atoms or
 4. A herbicidal composition according to claim 3 wherein R represents hydrogen or methyl; R1 is ethyl, isopropyl, cyclopropyl or 1-methylbutyl; R2 is hydrogen; R3 is methyl, ethyl, isopropyl or dimethylamino; n is 0 or
 2. 5. A method of controlling weeds according to claim 2 wherein R represents hydrogen or methyl, R1 is alkyl of two to five carbon atoms or cyclic alkyl of up to four carbon atoms, R2 is hydrogen or methyl, R3 is alkyl of up to three carbon atoms or
 6. A method of controlling weeds according to claim 5 wherein R represents hydrogen or methyl; R1 is ethyl, isopropyl, cyclopropyl or 1-methylbutyl; R2 is hydrogen; R3 is methyl, ethyl, isopropyl or dimethylamino; n is 0 or
 2. 